Seamless tiling of amorphous silicon photodiode-TFT arrays for very large area X-ray image sensors [digital radiography]

The authors propose a method for producing a truly seamless tiled image sensor from four identical subarrays, such that the resulting tiled image sensor has no missing pixels. Four standard amorphous silicon photodiode-TFT (thin film transistor) arrays are cut parallel to the busbars, in the space between the bus-bar and the preceding pixel electrode. The cut is done in such a may that it is adjacent to the pixel electrode on the active plate. The four subarrays are then rotated by 90°, with respect to their neighbors, and butted together. In this way, the seam between each tile has no adjacent bus-bar, and it is possible to reproduce the pixel pitch between neighboring tiles, with an acceptable alignment tolerance of the tiles. The authors have demonstrated the feasibility of the method, with the aid of a small prototype, based on a 192×192 pixel array, with a 200-μm pitch. Some image processing is necessary to rotate the images back for display on a conventional display monitor. This can cause artefacts, in some fast moving scenes, in which case an alternative scheme, which uses two mirror image arrays, each rotated by 180°, can be used. However, for static X-ray images and most images in dynamic medical X-ray applications this is not necessary and one can obtain good quality seamless images, free from any significant artefacts.